How much energy can solar panels produce in cloudy Britain?

solar panels

“But isn’t it too cloudy in Britain? There isn’t any sun…”

This is a very common question, and a perfectly sensible one – it’s clearly sunnier in the south of Spain than in Blackpool. The question is… by how much and does it matter?

At any given moment its not easy to predict how the weather is going to be, but throughout the course of the year, the overall sunniness level can be accurately measured and predicted. This value is called the insolation and can be defined as the amount of energy hitting a 1 square metre area pointed towards the sun over a whole year. In the South of England, according to the European Commission’s Joint Research Center, we get 1100 – 1200 kWh of irradiation per year (a kilowatt hour, kWh, is a typical unit of energy). In Devon and Cornwall you get between 1200-1300 kWh per year and in the North of England and Scotland its 1000-1000 kWh. In contrast, Barcelona gets 1700-1800 kWh of irradiation per year and in the very South of Spain and Italy it can get up to over 2000 kWh per year. So comparing London to Barcelona that’s 50% more irradiation for the Catalonians, which is significant but doesn’t mean we should give up hope for solar energy in the UK.

There are some other factors to consider here; sunniness doesn’t correspond exactly to the amount of solar energy you get out of a PV system. The best solar panels on the market today are only around 18% efficient under good conditions. At high temperatures for example, solar panels become less efficient. If the temperature of the solar panels increases by 20oC, they will only produce around 90% of the energy they would at room temperature. This means that on a clear but cold day in London, solar panels could produce more energy than a hot and sunny day in Spain.

Another factor is the difference between clear days and cloudy days. In the UK we get a lot of cloudy weather which blocks the sun and leads to ‘diffuse’ sunlight (meaning from all directions) rather than ‘direct’ sunlight. The four sunniest months of the year in the UK (May-August) deliver 5 times as much solar energy as the four winter months of the year (Nov-Feb). Solar panels can still turn diffuse light into electricity though, and there is evidence to suggest that some types of solar panels are better at collecting it than others. This means we may be able to improve the difference between London and Barcelona by using different technologies.

Despite these factors, solar panels in Spain will of course still produce more energy than solar panels in the UK, which makes energy from solar cheaper in Spain than over here. But in some ways what happens in Spain is irrelevant, the question that really matters is whether solar energy makes sense or not in the UK.

Dr Toby Ferenczi, our CTO, would say it does. With the feed-in-tariff, installing solar panels in the UK instantly becomes a highly profitable exercise yielding significantly better returns than most savings accounts (discussed in a previous article). Much of Germany, where over half the world’s solar panels are installed, is on the same latitude as the UK (northern Germany is in-line with Newcastle). So if it works over there, it should work over here.

The second point is that prices of solar energy systems are falling and electricity prices are continually rising, therefore leading to so called ‘grid parity’ – the point at which solar electricity costs the same as regular electricity and can flourish without government support.

Because Spain is sunnier, grid parity is expected to happen there sooner than here (some claim it may have already happened in certain cases). Several predictions indicate however (in particular those from the EPIA , the European Photovoltaic Industry Association) that we can expect grid parity in the UK as early as 2013 or 2014. So in just a few years solar energy will be competing on real terms with retail electricity prices, hardly a waste of time in my opinion.

The most important point is that the amount of sunlight that hits Britain is 50 times the total amount of energy we use (including the energy used for heating and transport). To get all of our electricity needs in the UK (50 units per person per day) we would need to cover 200m2 per person in solar panels. This is a large area, but feasible. So the next time someone greets you with incredulity at the prospect of using solar panels in the UK, you at least have some numbers to back yourself up.